Dihydroquinacridones are intermediates for the production of the well known quinacridone pigments like C.I. Pigment Violet 19, C.I. Pigment Red 202 and C.I. Pigment Red 122.
A number of patents describe processes for the direct synthesis of pigments in a pigmentary form to avoid the additional expensive and oftentimes environmentally unfriendly pigment finishing processes (e.g. processes for particle size reduction and/or crystal-form modification). For example, European Patent No.643,110 and U.S. Pat. No. 5,424,429 describe a direct synthesis of quinacridone solid solutions and 2,9-dichloroquinacridone in pigmentary form, respectively, in the presence of quinacridone phthalimidomethyl derivatives. European Patent No. 685,530 describes the direct synthesis of pigmentary grade dioxazine in the presence of a dioxazine derivative.
It is also known that sulfonic acid derivatives of certain pigments can effectively diminish the crystal growth during the isolation of the pigment from a reaction mixture. Such sulfonic acid derivatives are described, for example, in U.S. Pat. No. 3,386,843. Other patents describe the use of sulfonic acid derivatives of pigments to stabilize against recrystallization and change of crystal modification as, for example, in G.B. Patent No. 1,544,839 which is directed to phthalocyanine pigments.
U.S. Pat. No. 5,755,873 describes a method for the preparation of quinacridone pigments in which a quinacridone derivative is incorporated during synthesis and copending provisional application Serial No. 60/087,773 describes a direct synthesis of pigmentary diketopyrrolopyrrole pigments in the presence of quinacridone or diketopyrrolopyrrole derivatives.
Although the addition of such known pigment derivatives can be advantageous, pigment synthesis in the presence of such derivatives in many cases does not provide the favored pigmentary crystal size, shape or crystal modification.
Copending U.S. Provisional Patent Application entitled "PIGMENT PARTICLE GROWTH AND/OR CRYSTAL PHASE DIRECTORS", of the present inventor filed Feb. 2, 1999, discloses pigment particle growth and/or crystal phase directors which in many cases allow for the direct synthesis of pigmentary pigments without requiring a finishing step. However, these compounds themselves have coloristic properties and when used with certain pigments can behave as colored impurities and/or can reduce the saturation of the final pigment.
Japanese Patent No. 061 45 546 describes phthalimidomethyl dihydroquinacridones and the use thereof as pigment dispersants.